1. Field of the Invention
The field of the present invention is vessels used for and methods of transporting peracetic acid.
2. Background
Hazardous materials in the liquid state are often transported in stainless steel containers, particularly 316 stainless, because stainless steel is inert to many such hazardous materials. The Department of Transportation (DOT) regulates all such shipments to ensure public roadway safety, and the type of regulatory restrictions vary depending upon the hazardous nature of the liquid being transported.
For example, 49 C.F.R. 173.225 sets forth packaging requirements for organic peroxides, and indicates that a DOT-412 cargo tank may be used for transporting certain organic peroxides. The DOT-412 cargo tank has a nominal capacity of 5000 gallons, and is constructed according to the requirements set forth in 37 CFR 178.320, 178.345.,and 178.348.,the design specifications of which are incorporated herein by reference in their entirety. However, the DOT-412 cargo tank is not authorized for transporting peracetic acid, as this Type F organic peroxide, ID No. UN 3109 (as listed in 37 C.F.R. 172.101) is limited to a bulk containers having a capacity of up to 1,500 liters (396 gallons).
Requirements for the DOT-412 cargo tank include a 316 stainless steel container having a maximum allowable working pressure (MAWP) of not more than 40 psig and a resealable pressure relief system. According to regulations, the pressure relief system on a DOT-412 cargo tank is to have a set pressure to provide pressure relief at between 120%-132% of the MAWP and a minimum venting capacity based upon the exposed area of the cargo tank, which is typically provided by one 3″ reclosing pressure relief valve. The intent of these regulations is to equip the DOT-412 cargo tank with a sufficient size and quantity of pressure relief devices so that an increase in pressure of the cargo tank, whether due to a self-accelerating decomposition or fire engulfment, would not result in a rupture of the cargo tank.
The DOT can make exceptions to the regulations for the transport of hazardous materials over public roadways on a case-by-case basis. As one example, Azko Nobel Polymer Chemicals, LLC, of Chicago, Ill., has obtained an exemption for the transport of two types of Type F liquid organic peroxides, ID Nos. UN3109 and UN3119, both in Packing Group II, in a modified DOT-412 cargo tank. The modifications leading to approval of this special permit by the DOT include installation of six 12″ diameter non-reclosing pressure relief devices (in the form of rupture discs) as a single unit without being installed in series with a reclosing pressure relief device.
Due to the hazardous nature of the organic peroxide subject to the Azko exemption, which is more reactive than peracetic acid, which is also a Type F liquid organic peroxide, ID No. UN3109.,Packing Group II, and the increased risk of decomposition event if transferred in a standard DOT-412 cargo tank, the solution arrived at for the Azko special permit was to increase the overall pressure relief area to about 340 in2. Although peracetic acid would not likely require as much pressure relief area as specified in the Azko special permit, a significantly large pressure relief area would be required. In view of the large pressure relief area required, a different solution has been sought for a cargo tank to transport peracetic acid, one which could also be implemented by modifying a DOT-412 cargo tank, and one which would also meet the DOT goals of having pressure relief devices of a sufficient size and quantity so that an increase in pressure of the cargo tank, whether due to a self-accelerating decomposition or fire engulfment, would not result in a rupture of the cargo tank.